Port-access group (n=25), and lateral decubitus lung surgery group (n=25). Standard monitoring will be applied intraoperatively [electrocardiography (ECG), pulse-oxymetry (SpO2), invasive and non-invasive blood pressure]. After induction of anesthesia, an appropriately sized double lumen tube will be inserted and its position will be checked using fibroscopy. All patients will be placed on a volume controlled mode of ventilation with the following settings: tidal volume between 5 and 10 ml/kg and FIO2 at 50% and 4 cm H2O of positive end-expiratory pressure (PEEP). Respiratory frequency and tidal volume will be adjusted to maintain end-tidal carbon dioxide (ETCO2) between 30 and 40 mmHg. ETCO2 levels and SpO2 will be monitored continuously.